Adaptation of saccadic eye movements is necessary so that saccade accuracy can be maintained throughout life despite the changes caused by development, aging and trauma. The long-term objective of this grant is to study the possible role of the oculomotor vermis (OMV) of the cerebellum in the adaptation process. We will approach this objective with 3 sets of experiments. In the first, we will inactivate the OMV pharmacologically and determine the deficit in the behavioral adaptation of saccades to an intra-saccadic target step, which causes saccades to appear inaccurate. In the second, we will examine the behavior of simple spike activity in the Purkinje cells of the oculomotor vermis to determine how it changes during this behavioral adaptation. Finally, we will activate the putative error signal pathway that drives adaptation by stimulating the superior colliculus, which is the likely source of the error-related climbing fiber activity to the OMV. Because of the similarities of simian and human saccadic eye movement behavior, the results of this project should have considerable relevance in the diagnosis, treatment and rehabilitation of patients with saccadic eye movement disorders.